Hi! Thanks for the kind words, I’m glad it made you want to learn Sketch more. It’s an awesome tool!
Also, sorry for this late reply, for some reason I haven’t seen comments on my article :(
Regarding your question about why is it important to select the artboard instead of just the icon when exporting, it actually isn’t. Unfortunately, I wasn’t clear on this in the tutorial. What I wanted to show by selecting the artboard was the preview of the export on the right in the inspector where you can see the icon with the transparent background. It was more for the demonstration purposes, but it made things confusing.
Thanks so much for bringing this up, I was unaware of this mistake! I’ll make sure to fix it :)